Bumper systems generally extend widthwise, or transversely, across the front and rear of a vehicle and are mounted to rails that extend in a lengthwise direction. Many bumper assemblies for an automotive vehicle include a bumper beam and an injection molded energy absorber secured to the bumper beam with a fascia covering the energy absorber. The system including one or more members that connect the bumper beam to the vehicle chassis/frame is called the rail extension system. Beneficial energy absorbing bumper systems achieve high efficiency by building load quickly to just under the load limit of the rails and maintain that load constant until the impact energy has been dissipated. There is always a need to develop low cost, lightweight, and high performance energy absorbing systems that will deform and absorb impact energy to ensure a good vehicle safety rating and reduce vehicle damage in low speed collisions. Different components due to their inherent geometry and assembly requirements need different energy absorber designs to satisfy the impact criteria. Therefore, the automotive industry is continually seeking economic solutions to improve the overall safety rating of a vehicle. Hence, there is a continual need to provide a solution that would reduce vehicle damage and/or enhance a vehicle safety rating.
One such component can be a rail extension, which attaches the bumper system to the rails. An important aspect to be considered for a rail extension is the energy absorbed within the space available between the rail and bumper system. Depending upon the space available for a rail extension, the size and performance of the rail extension can vary. For example, a small space with a short rail extension can result in inadequate energy absorption. In addition, a large space with a long rail extension can result in unstable buckling instead of progressive crushing, which can lead to low energy absorption.
Polymeric rail extensions can suffer from a reduction in performance due to high temperatures. In addition, polymeric rail extensions can be damaged during a towing operation. Furthermore, polymeric rail extensions are limited in the materials that are available for electrophoretic deposition (e.g., e-coating). For example, only conductive polymeric materials are available for the e-coating process. In addition, for high speed crashes, polymeric rail extensions may not absorb similar energy levels as a metal rail extension. Rail extensions can also be limited by the method of manufacture. For example, injection molding of long part lengths prevents the inclusion of a generous draft angle. In addition, tool ejection becomes a challenge when using injection molding. Thus, it is difficult to provide structurally suitable reinforcements in specific areas within the rail extension when using injection molding techniques. As such, a need exists for a rail extension system that can perform at high temperatures and during towing operations. In addition, a need exists for a rail extension system that is not limited by material constraints. Finally, a need exists for a rail extension and a method of manufacture that can reduce the tooling costs and core length while allowing for the inclusion of crush initiators and reinforcing.
Vehicle rail extensions can slip against the bumper beam due to inadequate engagement resulting in an inefficient absorption of energy. In addition, bumper beams with a “B-shaped” cross section can clash on impact, resulting in the upper portion and lower portion crushing improperly and reducing impact absorption. As such, a need exists for a rail extension system that can reduce the unstable buckling and slippage of the rail extension and prevent clashing in order to increase the overall energy absorption of the system.